The invention relates generally to machines for supporting shaft-like workpieces, and the invention relates specifically to tailstocks on turning machines for machining shaft-like parts of rotation.
Research into the dynamics of machine tool structures, particularly that shown in treatise Machine Tool Structures, Vol. 1 by Koenigsberger and Tlusty, Pergamon Press, Copyright 1970, contains a compilation of analysis work of a variety of reseachers. Tlusty has shown that for a variety of horizontal bed, manual lathes, that the weakest portion of the machining area lies along a shaft held between a headstock and tailstock at the tailstock center. This portion may be further weakened when a live center is preferred over a dead center.
Additionally, Tlusty has shown that operations such as grooving are more difficult to perform at the tailstock end of a workpiece on a lathe. Tlusty's work shows that of all the lathes investigated, two significant modes of vibration or instability are connected with the workpiece axis. The one with the lower frequency is almost horizontal with a slight inclination, while that with the higher frequency is almost vertical with a slight inclination, i.e. approximately 90.degree. with respect to the first one.
Applicant has determined that, for example, on a horizontal bed machine, the turning process generates normal and tangential cutting forces on the workpiece, i.e. horizontal and vertical forces, (the resultant cutting force lying between the two). It has also been observed that most center support structures on tailstocks embody at least a snout for supporting a center quill and the snout is generally symmetrical (usually cylindrical) about the workpiece axis. Even on machines where a square snout is employed, the horizontal and vertical dimensions are identical. Therefore, these machines tend to have identical compliance of the snout/quill/center system in the vertical and horizontal directions. Applicant has determined that a far superior dynamic stability can be achieved by the inventive design, which provides for nonsymmetry between the tangential and normal cutting directions at the tool point. Specifically, applicant has determined that a massive, solid quasi-rectangular cross-section is most desirable for increasing machine stability at the tailstock end of the workpiece.
Workpiece size plays a great part in the overall dynamics of the turning machine stability, and applicant has considered that specific quill support cross-sections may be configured and sized for a given workpiece to be supported, but in commercial application, a machine must be capable of handling a variety of workpieces. Therefore, the range of workpieces to be handled has necessitated applicant's optimization of a tailstock support system, wherein the modes of compliance of the tailstock are coupled with the compliance of the workpiece to provide an outstanding support system.
Additionally, applicants have configured the tailstock support system so that the machine may be configured as a two-axis lathe, i.e. where a tool slide system moves a tool axially and radially with respect to a workpiece. Optionally, the machine may be configured as a four-axis machine, where a substantially identical slide system is used on the opposite side of the workpiece so that simultaneous machining operations may occur.
It is a therfore an object of the present invention to provide a tailstock support system having improved dynamic stability characteristics.
Another object of the present invention is to provide a tailstock support system wherein the tailstock center is suported in a noncylindrical beam section.